1. Field of the Invention
This invention relates in general to devices and method for treating metals and in particular to a new and useful process and device for heating non-ferrous metal strips.
2. Description of the Prior Art
It is current practice to heat metal strips continuously while they are transported without contacting them, whereby transport velocities, according to thickness of the strip, of up to 120 m/min. can be reached for the strip. Heating units provided with gas jet nozzles are used to carry out the heating without the strips coming into contact with any transport element. Such heating units, for example, have been successfully employed in the strip and light metal industry. The heat treatment should advantageously uniformly transfer a large amount of heat in a short time to the material to be heated, and also transport the strips without contact.
It is essential for the known embodiment that the strip coming from the coiling reel passes through a looping tower, then through an S-roller unit or aggregate and finally horizontally through the continuous furnace again through an S-roller aggregate onto which joins a second looping tower and the coiling reel. In order to guarantee a continuous operation, two discharge reels and two coiling reels must both be provided in combination with the looping towers and the strip tacking means.
There are also units which are not operated continuously so that these duplicate reels and looping towers can be abandoned. In this case a shutdown period results due to the necessity for tacking or welding of a new metal strip. This shutdown period influences the heat treatment condition of the metal strip in the heat zone, thus providing a greater accumulation of scrap.
If it is taken into consideration that the gas jet furnaces, e.g., in high speed units, for aluminum can be up to 150 m in length, then it is found that the continuous operation has advantages despite the expense of the units, because the accumulation of the scrap is less.
It has also been proposed to heat metal strips and sheets inductively (British Pat. No. 600,673) by passing these products between parallel and spaced groups of induction coils. To the applicants' knowledge such units have not proved themselves in practice for heating metal sheets and strips.
A further proposal is to heat foils electrically directly by contact by means of a circulating roller, by pressing the foils by means of deflection rolls against a section of the circulating roller. The roller itself is heated on the reversed section through using magnetic rotary fields. Unequal heating of the roller is counteracted by different spacings between the rotary field and the roller, so that the foil heated by contact is also uniformly heated (German Offenlegungsschrift No. 2,204,816). This proposal is not suitable for heating without contact.